The Chronology of Exodus
The book of Shemos-Exodus comes to an end this Shabbos with the reading of parshas Pikudei.
Shemos-Exodus features three main interconnected themes:
The first is the Exodus of the Jewish people from Egyptian bondage. The second is the giving of the Torah at Mount Sinai and the third is the construction of a Sanctuary, the Mishkan, through which G‑d would dwell amongst the people.
The ultimate goal for the Jewish people is for them to forge a unique relationship with G‑d so that He would dwell among them and, through them, the entire world.
The first four sections of Exodus recount the enslavement of the Jewish people, the Ten Plagues, the Exodus and the splitting of the Red Sea, which finalized the Exodus.
The Exodus from Egypt occurred on the 15th day of the month of Nissan in the year 2448.
The next two sections of Shemos detail the giving of the Torah at Mount Sinai, when G‑d declared the Ten Commandments (more precisely: The Ten Statements) followed by many laws that extended the original Ten Statements. This took place 50 days after the Exodus, on the sixth of Sivan.
The next four sections of Shemos discuss G‑d’s directives to Moses to command the Jewish people to contribute towards and construct the Mishkan and the details of the construction of the Mishkan and its vessels. The Torah also recounts how, while Moses was on the mountain, the Jewish people constructed and worshipped a Golden Calf, which transgression drove Moses to shatter the Tablets he had just brought down from Mount Sinai after his encounter with G‑d.
This shattering event occurred on the 17th of Tammuz, only forty days after the people heard the Ten Commandments directly from G‑d.
This Parsha then relates how Moses went back up onto Mount Sinai for another period of 40 days to procure G‑d’s forgiveness of the Jewish people and prepare a second set of Tablets. After a third period of 40 days, Moses descended with the second set on the 10th of Tishrei, the day now designated as Yom Kippur.
It was on the very next day that Moses gathered the Jewish people and conveyed the command to contribute for the Mishkan.
The final Parsha of Shemos (Pikudei), after providing an accounting of all the materials in the Mishkan and its actual construction, then discusses the dedication of the Mishkan.  That took place on the first day of the Month of Nissan, almost six months after Moses brought them the command to build it.
The command to construct the Mishkan was G‑d’s way of saying that, notwithstanding their transgression with the Golden Calf, He would dwell in their midst. G‑d demonstrated His willingness to forgive the people by giving Moses a second set of Tablets on Yom Kippur, 120 days after the Torah was initially given, and then agreeing to dwell among them through the construction of the Mishkan.
Postponed Dedication 
There is one serious problem with this chronology. It concerns the day the Mishkan was dedicated.
According to the Midrash it was built in less than three months and completed on the 25th day of Kislev. Yet, it was not erected and dedicated until the first of Nissan. According to that Midrash, G‑d “compensated” and “appeased” the 25th day of Kislev, which should have been the day the Mishkan was dedicated, by having the rededication of the Second Temple during the Chanukah era occur on the 25th day of Kislev.
This postponement of the dedication of the Mishkan prompted the Midrash to ask why not dedicate it right away, as soon as it was completed on the 25th of Kislev? Why did G‑d ask the people to wait until Nissan to dedicate the Mishkan?
The Midrash’s answer is that the Patriarch Isaac was born in the month of Nissan and G‑d wanted the Sanctuary to be built in the month of his birth.
Isaac the Model of Sacrifice
However, this explanation raises another question: According to the Talmud, all of the Patriarchs were born in the month of Nissan. Why then does the Midrash single out the birth of Isaac as a reason for postponing the dedication of the Mishkan to the month of Nissan? There must be some deeper connection between Isaac and the Mishkan.
One simple explanation offered by commentators is that Isaac represents the concept of sacrifice. Isaac was offered as a sacrifice on Mount Moriah, the eventual site of the Bais Hamikdash which, according to our Sages, serves as a force of atonement for his progeny, the Jewish people.
Therefore, the Mishkan, the place where sacrifices would be offered, and which would bring atonement to the Jewish people, had to be dedicated in a month associated with Isaac, who personified sacrifice and the dynamic of atonement.
“In the Future, We Will Say to Isaac, You are Our Father!”
One can find a deeper connection between Isaac and the role of the Mishkan with respect to their power to atone for the Jewish people based on a Biblical statement (Isaiah 63:16) that in the future Messianic Age we will refer to Isaac, exclusively, as our father.  This statement is explained in the Talmud (Shabbos 89b) by referring to a dialogue G‑d will have with all three Patriarchs concerning the fate of the Jewish people.
When G‑d approaches Abraham and reports to him the sins of the Jewish people he responds, “Let them be erased for the sanctification of G‑d’s name!”  G‑d elicited the same response from Jacob. Only Isaac seeks to negotiate with G‑d on behalf of his children and as a result brings about their atonement.
It is unfathomable to think that Abraham, the paragon of kindness and love, would wish his progeny to die for the sanctification of G‑d’s name. Likewise, it is difficult to comprehend how Jacob, who personified the trait of compassion, can reconcile his compassion for his children with a death wish for them, no matter how egregious their sins.
It maybe suggested that Abraham and Jacob were not going to consign their children to death, G‑d forbid. On the contrary, they were going to offer G‑d a defense for their children whom G‑d was indicting for iniquity.
They were, in effect, going to say, “Look, how wonderful your children are. Despite their sinful behavior, You, G‑d, know that they would be willing to die if given a choice of apostasy or death. They would gladly give their lives for the sanctification of G‑d’s name if it came to such a test.” Indeed, throughout history there were countless Jews, many of whom not observant, who died rather than betray their belief in one G‑d. This, Abraham and Jacob argue, points to the inner and intrinsic goodness and holiness of every Jew, even those Jews who have outwardly deviated from the Jewish path.
But to bring about the Final Redemption G‑d will not be content with our inner goodness. When dealing with our state of Jewishness in the past, we could point to our spiritual potential; we may be prepared to give our lives for G‑d even if we fail to live a complete G‑dly life. But, as we come closer to the Messianic Age when the world must become a dwelling place for G‑d and we have no time to waste, it does not suffice for our inner good to be intact. It is crucial that we come to greet Moshiach with both internal and external righteousness. Mitzvos are referred to as our garments, and when we greet a king, we must be dressed immaculately. As we approach the final Redemption, when G‑d’s presence will pervade the entire world, we must go to the next step and demonstrate that we are a good and holy people overtly just as we are innately.
Thus, Isaac’s approach finds favor in G‑d’s eyes because Isaac, the man who personifies judgment, analysis and scrutiny, seeks and discovers our external good as well. Once he discovers the external good, he is in the position to negotiate with G‑d about our external flaws and find justification for our redemption.
This ties in with the statement in the Talmud (end of Chagigah) that “even the sinners of Israel are filled with Mitzvos as a pomegranate is filled with seeds.” This statement is not just theoretical talk about some inner, potential Mitzvos but actual ones. Isaac insists that we have both inner and outer beauty and we are therefore worthy of Redemption. 
Inner and Outer Beauty for the Mishkan
We can now understand why G‑d waited for the month of Nissan to dedicate the Mishkan: it is the month of Isaac’s birth.
Isaac is unique in that he beholds the way the Jewish people exhibit both inner and outer beauty.
When Moses built the Mishkan it was as a place where G‑d would feel “comfortable” living amongst the Jewish people. To make G‑d comfortable requires that the Mishkan, and subsequently the Bais Hamikdash, represent and reflect the Sanctuary within the heart of each and every Jew.
Even so, the fact that we all have a Sanctuary for G‑d in our soul it does not suffice. The objective is that Sanctuary be expressed in our every thought, speech and action. When that occurs, Isaac, the Patriarch known for and identified with the attribute of Gevurah-judgment, will be excited and vouch for us, so that we can be redeemed immediately from exile and witness the construction of the third Bais Hamikdash, at which time we will all declare, “Isaac, you are our father!”